One of Prime Minister Shinzo Abe's top advisers says he favors a declaration by Japan's policymakers that their current measures are monetizing the nation's debt.

Some people say that Japan has "already adopted ad hoc monetization of debt, and that to improve public confidence the government and the Bank of Japan should recognize that they are doing already a combination of fiscal stimulus and de facto monetization," Koichi Hamada, a former Yale University professor, said in an emailed response to questions.

"Given this long deflation and liquidity-trap type of behavior of Japanese banks and firms, I am now inclined to join the ranks" of those commentators, Hamada said. That view says "piecemeal and de facto monetization should be rather highlighted to change investors' psychology," he said.

Hamada declined to comment specifically on the BOJ's decision Friday to conduct a "comprehensive" assessment of its measures at its next meeting, or whether it's likely to expand stimulus further at that gathering, which is scheduled for Sept. 20-21.

The adviser also reiterated his opposition to "helicopter money." "If one institutionalizes helicopter money or monetization of the new debt, the economy loses the safeguard against inflation."

Through its easing to date, the BOJ has gobbled up more than one-third of outstanding Japanese government bonds, and some observers do not anticipate that debt will ever return into the hands of private investors. BOJ officials in the past debated a strategy of maintaining a large balance sheet — at least back in 2014, according to people familiar with the talks at the time. The context then was to avoid any spike in bond yields when the central bank reached its inflation target.